Comparison of sedimentary processes on adjacent passive and active continental margins offshore of SW Taiwan based on echo character studies

Abstract

Echo character recorded on Chirp sub-bottom sonar data from o¡shore of SW Taiwan was analysed to examine and compare the sedimentary processes of adjacent passive and active continental margin settings. Sea£oor echoes in the study area are classi¢ed into four types: (1) distinct echoes, (2) indistinct echoes, (3) hyperbolic echoes and (4) irregular echoes. Based on the mapped distribution of the echo types, the sedimentary processes o¡shore of SW Taiwan are di¡erent in the two tectonic settings. On the passive South China Sea (SCS) margin, slope failure is the main process on the upper continental slope, whereas turbidite deposits accumulate in the lower continental slope. In contrast, the submarineTaiwan orogenic wedge is characterized by ¢ll-and-spill processes in intraslope basins on the upper slope, and mass-transport deposits are observed in the canyons and on the lower Kaoping slope.This di¡erence is largely caused by the huge in£ux of terrigenous sediments into the submarineTaiwan orogenic wedge compared with the passive SCS continental margin. In the latter, loading and movement of theTaiwan orogenic wedge has had a signi¢cant e¡ect on the sea£oor morphology and has triggered retrogressive failures. Gas hydrate dissociation may have enhanced the slope failure processes at some locations.

The northeastern South China Sea margin created by the combined action of down-slope and along-slope processes: Processes, products and implications for exploration and paleoceanography

“…1 and 2). The study area is strongly dissected by deep-marine erosive channels, submarine canyons, and slope gullies, all of which act as active conduits for the delivery of clastic sediments from South China Sea shelf and/or upper slope into deep-marine environments (Chiu and Liu, 2008;Gong et al, 2013;Fig. 2 (Qu et al, 2006;Yang et al, 2010;Gong et al, 2013;He et al, 2013;Fig.…”

“…The study area is located along the northeastern South China Sea margin and can be divided into two distinctive tectonic provinces, the South China Sea passive continental margin and the Luzon subduction complex (Chiu and Liu, 2008;Figs. 1 and 2).…”

Imaging P- and S-wave velocity structures in hydrate bearing sediments along an OBS profile across the Yuan-An Ridge, off southwest Taiwan

“…The depth-integrated anaerobic oxidation of methane and sulfate reduction rates were more comparable and were similar to sites studied in the Black Sea, Sea of Okhotsk, and the Namibian shelf where upward fluid flow is absent (Chuang et al 2013). By integrating marine geophysical results together with geological and geochemical information derived from analyzing core samples, Chiu and Liu (2008) suggest that the Yung-An Ridge area may possess three different types of gas hydrate reservoirs. Wide spread occurrence of bottom simulating reflectors (BSRs) observed in the Yung-An Ridge area indicated the presence of gas hydrates and thus sufficient supply of methane and water Hsu et al 2018b).…”

Recent sedimentary processes along the Makran trench (Makran active margin, off Pakistan)

“…Echocharacters studies have been widely used in order to determine sediment processes in various deep-sea environments, frequently in passive margin context (Jacobi, 1976;Embley and Langseth, 1977;Damuth, 1980a;Damuth and Flood, 1985;Pratson and Laine, 1989;Damuth, 1994;Gaullier and Bellaiche, 1998;Loncke et al, 2002), but more rarely in convergent margin contexts (Henry et al, 1990;Whitmore et al, 1999;Chow et al, 2001;Chiu and Liu, 2008). The more rugged seafloor and the higher slope values generally observed in such environment may disturb acoustic acquisition and explain the lack of interest in using echo-character mapping in convergent margin context.…”